A human voice sound is produced by a physical mechanism that involves air-flow from the lungs of the individual through the structures that comprise the vocal tract of the individual. The production of the human voice sound is a complex nonlinear process that depends on the shape of the human vocal tract. The vocal tract shape is dependent on a bone structure, body size, race, age, and so forth of an individual. The relative shape of the vocal tract resonant cavities, the vocal tract tissue structure and density, and other factors such as lung capacity (controlling air-flow dynamics through the vocal tract), inertia of movement of the vocal apparatus etc. can also contribute to the sound of the human voice. The combination of these complex factors result in voice sounds that can be unique to the speaker.